The decisive question on this appeal is whether the court erred in overruling defendants’ motion for nonsuit.
The doctrine of res ipsa loquitur is not invoked by plaintiff, nor is it available. The attic furnace, the underground tanks, filler pipes, and the entire store building were under the control of the plaintiff. The doctrine does not apply when the instrumentalities causing *492the injury are not under the exclusive control or management of the defendant. Nor does the doctrine apply “where more than one inference can be drawn from the evidence as to the cause of the injury, (or) . . . where the existence of negligent default is not the more reasonable probability. . . .” Springs v. Doll, 197 N.C. 240, 148 S.E. 251. Therefore, the plaintiff must present evidence of actionable negligence on the part of the defendant in order to carry his case to the jury. To establish actionable negligence plaintiff “must show: (1) That there has been a failure on the part of defendant to exercise proper care in the performance of some legal duty which defendant owed to the plaintiffs under the circumstances in which they were placed; and (2) that such negligent breach of duty was the proximate cause of the injury, a cause that produced the results in continuous sequence, and without which it would not have occurred, and one from which any man of ordinary prudence could have foreseen that such result was probable under all the facts that existed. . . . Negligence is not presumed from the mere fact of injury. . . . There must be legal evidence of every material fact necessary to support a verdict, and the verdict ‘must be grounded on a reasonable certainty as to the probabilities arising from a fair consideration of the evidence, and not a mere guess, or on possibility’ ... If the evidence fails to establish either one of the essential elements of actionable negligence, the judgment of nonsuit must be affirmed.” Lane v. Dorney, 250 N.C. 15, 108 S.E. 2d 55; Lane v. Dorney, 252 N.C. 90, 113 S.E. 2d 33; Reason v. Machine Co., 259 N.C. 264, 130 S.E. 2d 397.
Plaintiff, in support of his allegations, attempts to show by direct and circumstantial evidence that defendants were negligent in that their agent, Hamilton, (a) attempted to deliver gasoline during the dark and prior to daylight hours, (b) attempted to deliver gasoline into underground tanks when the weather was dense, foggy, and heavy, and the air was still, (c) left the vehicle unattended while delivering a hazardous and dangerous substance, (d) allowed or permitted gasoline to overflow or leak from the filler pipes or hoses onto the driveway in large quantities, creating an extremely dangerous and hazardous condition.
Plaintiff offered direct evidence which tended to sustain his allegation that defendants left the truck and tanker unattended after starting delivery of gasoline; that the weather was dense, foggy and heavy, and the air still, and that the delivery was made prior to daylight hours. Plaintiff seeks to show by circumstantial evidence that defendants’ agent negligently allowed gasoline to spill or leak in front of the store building, and that the leakage or spillage was the proximate cause of the explosion. His theory is that as *493the spilled gasoline evaporated during a period of ten or fifteen minutes, vapors from it traveled through a vent into the attic, where they were drawn into the fresh-air inlet of the furnace and to the open flame, thereby causing the explosion.
The only evidence of spilled gasoline near the filler pipes and in front of the store was the testimony of plaintiff’s witness Shew, who testified, over defendants’ objections, substantially as follows: That he was some three-quarters of a mile from the plaintiff’s store when he saw a flash in the sky above the store. He immediately proceeded to the store, and arrived there about one minute later. “I saw some guy — I don’t know who he was — at the tanker. He was at the back unhooking a hose. One was already unhooked from the tanker. The other hose was already loose. It was laying beside the tank, . . . He got in his tanker and left. ... he came back up there ... in a short time and took the hoses out of the tank ... we pulled one down next to the gas tank and we carried the other one across the road to the mail box.” Question by plaintiff’s attorney: “Now when you went to help him pull the pipe away — or pull the hose away, what was he doing at that time at the filler pipe? A. He pulled the hose out and was putting a cap on it.” Question by plaintiff’s attorney: “. . . at the time you were there at the filler pipes, did you make an examination around the filler pipe and leading from the filler pipe down the highway? A. No, I didn’t exactly make an examination. I just noticed there was some gas had run down through there. . . . There was no fire out in front of the store anywhere along that whole area at that time.”
Plaintiff also offered the testimony of Charles Harmon, who was, over defendants’ objection, qualified as an expert in the field of thermo dynamics, gas dynamics, and gas combustion. Over defendants’ objection, plaintiff’s counsel asked him a hypothetical question as to what might or could have caused the explosion and fire. This question contained, inter alia, the following two hypotheses: “10. That during the period that the tanker was unloading its gasoline into the storage tank the strong odor of gasoline was smelled. 11. That prior to the time that the tanker began the unloading of gasoline there was no gasoline on the ground in the area of the filler pipes or in front of the building.” In answer, Mr. Harmon said: “It is my opinion that the explosion and resulting fire could or might have resulted from gasoline vapors in the correct proportion to cause an explosive mixture. That such a mixture came in contact with the open flame of the hot air furnace, and that this vapor entered the attic space where the furnace was through the louvered ventilator, and that the vapor came from the evaporation *494 of spilled gasoline in front of the store.” (Italics ours) Defendants’ motion to strike this answer was overruled.
“Expert opinion derives its probative force from the facts upon which it is predicated, and these must be legally sufficient to sustain the opinion of the expert. . . . The facts on which an opinion is based must measure up to legal requirements. Expert testimony on a state of facts not supported by the evidence is inadmissible.
“Expert testimony on speculation or conjecture is not evidence, especially when it conflicts with physical facts. . . . The expert’s opinion cannot be elicited to supply the substantive facts necessary to support the conclusion.” (Italics ours) Rogers on Expert Testimony, Third Edition, § 54, pp. 109, 111.
“The objection to the admission of opinion evidence of expert witnesses on the ground that in the particular instance it invades the province of the jury has been expressed by this Court in several decisions. . . . ‘Whatever liberality may be allowed in calling for the opinions of experts or other witnesses, they must not usurp the province of the court and jury by drawing conclusions of law or fact upon which the decision of the case depends.’
“However, it would seem that the proper test is whether additional light can be thrown on the question under investigation by a person of superior learning, knowledge or skill in the particular subject, one whose opinion as to the inferences to be drawn from the facts observed or assumed is deemed of assistance to the jury under the circumstances. . . . Undoubtedly it would be competent for an expert witness to give his opinion as to what causes would produce the result observed, but this would not permit him to inject into the consideration of the jurors the weight of his assertion that such result was in fact produced by a particular cause.” Patrick v. Treadwell, 222 N.C. 1, 21 S.E. 2d 818.
It was competent for the expert witness to express an opinion that gasoline vapors coming in contact with the open flame in the attic furnace could have produced the explosion, but it was beyond his province as a witness to state to the jury as a fact that the explosion was caused by vapors that came from the evaporation of spilled gasoline in front of the store. Expert opinion testimony is no stronger than the facts upon which it is based, and evidence based on guess, conjecture or speculation should be disregarded. The objection to the hypothetical question should have been sustained and the answers stricken, because of the insufficiency of evidence showing that gasoline spilled Before the explosion. On the contrary, the evidence suggests that it was spilled After the explosion when Hamilton disconnected the hose. Although incompetent, this evidence must be considered for whatever it is worth in passing upon *495the motion for nonsuit. Assuming that the gas was spilled in front of the store, the crucial question remains as to When it was spilled.
Plaintiff’s expert witness further testified: “Evaporation is affected by the temperature so that if the gasoline is cold, it will evaporate more slowly than if it is hot. If the outside temperature is cold, rather than warm, it will evaporate more slowly cold than warm. ... I would say that some of the important factors in determining the question as to whether the presence of gasoline vapors in an area would be the size of the area covered; the time it had been there in existence; the temperature of the ground and the air, and of the gasoline itself; and finally, whether or not there was any wind, motion or anything to carry it away; ... If an area is covered with gasoline and the air is completely still, the evaporation is going to be slower than if there is a wind blowing across it; gasoline vapors are three to four times heavier than air. . . . Assuming that the jury finds from the evidence that the regular gas tank, or one of the regular gas tanks, or tanks holding regular gas, underneath the store was a 4,000 gallon tank and was empty, then for each gallon of gasoline put into that tank there would necessarily be a gallon of air or gasoline or vapors expelled from the tank. . . . Taking my theory about the fumes going into the combustion chamber and there being ignited by the flame, then the explosion would propagate out to wherever these fumes were present. This propagation would be on the order of thousandths of a second, perhaps. When you have ignition anywhere in a volume of fumes, it is going to propagate to the end of those fumes immediately, using the term immediately in the ordinary sense. . . . The ignition of a flammable mixture of gasoline vapors will propagate to the point where the flammable mixture is no longer a flammable mixture. And if the flammable mixture extended from the point of ignition to the source of the gasoline fumes, then it would propagate right down to the source of the gasoline.”
All of plaintiff’s evidence shows that there was no fire in front of the store for an appreciable length of time after the explosion. Yet, plaintiff contends that the source of the fumes or vapors which caused the explosion came from in front of the store building.
It is more plausible to infer from plaintiff’s evidence that as gasoline was received in the underground tanks vapors were expelled from the tanks through the vent pipes into the attic, where they were ignited by the furnace, or into the refrigeration equipment room where they were ignited by the electric motors.
The only evidence which plaintiff offered to sustain his allegations of defendants’ negligence was that tending to show that Hamilton left the tanker unattended after starting the flow of gasoline. *496Plaintiff failed to show, however, that defendant Hamilton’s absence or his failure to have the truck attended caused gasoline to spill or leak in front of the store. Without some evidence that Hamilton had caused or permitted gasoline to spill before the explosion, plaintiff cannot establish such negligence as a proximate cause of the explosion, and his allegation fails.
“There must be some causal relationship between the breach of duty and the injury.” Reason v. Sewing Machine Co., 259 N.C. 264, 130 S.E. 2d 397.
The plaintiff relies heavily on the case of Moore v. Beard-Laney, Inc., 263 N.C. 601, 139 S.E. 2d 879, in which the agent of the defendant was delivering gasoline to the plaintiff’s service station, and the agent had been warned that one of the tanks might overflow, that it was necessary to watch the air vent on the tank in order to see when the tank was full. Notwithstanding, after the agent started pumping gasoline for delivery, he went into the store and while he was in the store the tank overflowed; the gasoline was ignited by a spark from an electric switch, causing damage. The Court held these facts sufficient to be submitted to the jury on the issue of negligence. The Moore case, however, is distinguishable from the instant case, in that there the plaintiff not only offered direct evidence that the tank had overflowed before the explosion, but that defendant had been warned of the danger. There was also direct evidence that the gasoline which had overflowed was ignited by a spark from an electric switch. Comparable evidence is lacking here. Plaintiff has failed to offer any evidence that the explosion was caused by the actionable negligence of defendants.
The motion for nonsuit should have been allowed. The judgment below is
Reversed.